I'm sort of at a refining stage in my space program. I can't claim I pay attention to TWR per se throughout my launch, but obviously at least 1 to begin getting off the ground. I have a design now that is just massive rings of concentric boosters, and its been able to get me anywhere, but I'm running into a few problems. So by the time I have a stable kerbin orbit, I've got about 1500 m/s left on a ring of six red boosters around my central craft, which is enough to begin but not finish long distance transfer burns. At that point the plan is to switch to 10 nuclear engines, but even with 10 since the ship is so heavy, I find that the burns are so slow that I miss my window and end up having to do expensive mid course corrections. I'm leaning away from using nuclear stuff to inject large objects on far trajectories, because quite simply it goes too slowly. Of course, in not doing so I miss out on a lot of delta V. You don't really NEED it, but now I shoot for at least .80 TWR for injection. Though of course my upper stage with six nuclear engines injects pretty fast, but each engine only has an FLT-200 to draw from.